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In a paper (PDF of full article) which has been accepted for Geophysical Research Letters, NASA researchers
created a suite of 3-dimensional climate simulations using topographic data from the Magellan mission, solar spectral irradiance estimates for 2.9 and 0.715 billion years ago, present-day Venus orbital parameters, an ocean volume consistent with current theory and measurements, and an atmospheric composition estimated for early Venus.
According to the output of the general circulation model, "Venus may have had a climate with liquid water on its surface for approximately 2 billion years." In the simulation, extensive, highly reflective, H2O clouds formed on the lit side of the planet. "A strong day-night circulation" carried heat to the dark side. These factors limited the range of temperatures, in spite of a slow rotation rate. The authors note that liquid water can be not only a sign of habitability, but a cause of it:
[...] while the possibility of surface liquid water defines the traditional habitable zone, our results suggest that a planet with a modest amount of surface liquid water is more conducive to habitability over a wide range of stellar fluxes than a planet largely or completely covered by water. The inner edge should therefore be considered a transition region in which the probability of habitability gradually decreases inward rather than a strict boundary separating completely different regimes.
Venus today has little water. The high ratio of deuterium to protium (as compared to the ratio in Earth's surface water) leads us to believe that large most of the planet's hydrogen has escaped to space.
in the popular press:
(Score: 0) by Anonymous Coward on Monday August 15 2016, @10:59PM
Well, they gave a poster of their model this year [confex.com].
I have to disagree on the level of detail. Their model is a derivative of the ModelE2-R model, not a whole new model, so one can take it to be sufficiently similar. As for Table 1, they list in great detail the inputs they used for each scenario modeled. Not only in the table caption, but in the paragraph which references the table.
I'm not sure I get your point about conservation of energy. Do you have reason to think these models don't conserve energy? The Schmidt paper goes into great lengths on the involved physics.
(Score: 1, Interesting) by Anonymous Coward on Monday August 15 2016, @11:23PM
Yes, I have recently been playing with solar system models and learned that this is an issue even when modelling much simpler systems like that. It is used as a basic check that the numerical integrations being performed can correspond to something physical (it doesn't prove they are working right if energy + angular momentum is conserved, but it proves something is wrong if large deviations are detected). I wanted to see how they dealt with energy conservation, especially using such large timesteps (4 hrs).
I glanced at the Schmidt paper and saw no plots showing (E_0 - E_t ~ 0) or anything of that nature, then decided it should be included in this paper anyway because "derived from" is too vague a description of the modifications.